Advanced military and proposed commercial aircraft, shuttle craft, and other extraterrestrial craft have what are known as fly-by-wire control systems. Manipulation of the control at a pilot's station results in the generation of an appropriate electrical control signal. This signal is transmitted to an onboard computer. The computer outputs a signal for operating a typically hydraulic control surface actuator to effect the wanted displacement of the involved control surface.
A sidestick controller is one type of device that is employed at pilot stations in craft equipped with fly-by-wire control systems. Heretofore available sidestick controllers have a control stick mounted for pivotable movement in the inboard and outboard directions about a fore-and-aft axis paralleling the longitudinal axis of the craft in which the control stick is installed. By rotating his hand in a clockwise direction, a pilot can pivot the sidestick controller in the same direction. Acting through a mechanical linkage of the parallelogram type, this causes an associated transducer to produce an electrical signal which results in the craft rolling to the right about its longitudinal axis. The degree of roll and roll rate are determined by the magnitude and rate of displacement of the sidestick. Similarly, by rotating his hand in a counterclockwise direction, the pilot can cause the craft to roll to the left at the wanted rate and through the wanted angle.
In craft with two pilot stations, a sidestick controller is located at each station; and the controllers are mechanically connected. This allows the roll of the craft to be controlled from either of the pilot stations.
As heretofore designed, the sidestick linkage was so constructed that the force required to rotate the sidestick in the outboard direction (counterclockwise for the pilot and clockwise for the copilot) and in the inboard direction were equal. Because of the anatomical construction of the human arm, however, greater effort is required to displace the sidestick through a given arc in the outboard direction than is required to rotate that control element through the same arc in the inboard direction. As a result, pilot forearm, wrist, and hand fatigue become a real concern.